Network Working Group S. Floyd, Ed.
Request for Comments: 5166 March 2008
Category: Informational
Metrics for the Evaluation of Congestion Control Mechanisms
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
IESG Note
This document is not an IETF Internet Standard. It represents the
individual opinion(s) of one or more members of the TMRG Research
Group of the Internet Research Task Force. It may be considered for
standardization by the IETF or adoption as an IRTF Research Group
consensus document in the future.
Abstract
This document discusses the metrics to be considered in an evaluation
of new or modified congestion control mechanisms for the Internet.
These include metrics for the evaluation of new transport protocols,
of proposed modifications to TCP, of application-level congestion
control, and of Active Queue Management (AQM) mechanisms in the
router. This document is the first in a series of documents aimed at
improving the models that we use in the evaluation of transport
protocols.
This document is a product of the Transport Modeling Research Group
(TMRG), and has received detailed feedback from many members of the
Research Group (RG). As the document tries to make clear, there is
not necessarily a consensus within the research community (or the
IETF community, the vendor community, the operations community, or
any other community) about the metrics that congestion control
mechanisms should be designed to optimize, in terms of trade-offs
between throughput and delay, fairness between competing flows, and
the like. However, we believe that there is a clear consensus that
congestion control mechanisms should be evaluated in terms of trade-
offs between a range of metrics, rather than in terms of optimizing
for a single metric.
Floyd Informational [Page 1]RFC 5166 TMRG, METRICS March 2008Table of Contents
1. Introduction ....................................................2
2. Metrics .........................................................3
2.1. Throughput, Delay, and Loss Rates ..........................4
2.1.1. Throughput ..........................................5
2.1.2. Delay ...............................................6
2.1.3. Packet Loss Rates ...................................6
2.2. Response Times and Minimizing Oscillations .................7
2.2.1. Response to Changes .................................7
2.2.2. Minimizing Oscillations .............................8
2.3. Fairness and Convergence ...................................9
2.3.1. Metrics for Fairness between Flows .................10
2.3.2. Metrics for Fairness between Flows with
Different Resource Requirements ....................10
2.3.3. Comments on Fairness ...............................12
2.4. Robustness for Challenging Environments ...................13
2.5. Robustness to Failures and to Misbehaving Users ...........14
2.6. Deployability .............................................14
2.7. Metrics for Specific Types of Transport ...................15
2.8. User-Based Metrics ........................................15
3. Metrics in the IP Performance Metrics (IPPM) Working Group .....15
4. Comments on Methodology ........................................16
5. Security Considerations ........................................16
6. Acknowledgements ...............................................16
7. Informative References .........................................17
1. Introduction
As a step towards improving our methodologies for evaluating
congestion control mechanisms, in this document we discuss some of
the metrics to be considered. We also consider the relationship
between metrics, e.g., the well-known trade-off between throughput
and delay. This document doesn't attempt to specify every metric
that a study might consider; for example, there are domain-specific
metrics that researchers might consider that are over and above the
metrics laid out here.
We consider metrics for aggregate traffic (taking into account the
effect of flows on competing traffic in the network) as well as the
heterogeneous goals of different applications or transport protocols
(e.g., of high throughput for bulk data transfer, and of low delay
for interactive voice or video). Different transport protocols or